The long-term goals of this research are to understand the structure, assembly, and function of cilia and flagella, and their roles in human health. The studies are utilizing Chlamydomonas and mice as model organisms, and are focused on processes and proteins that are highly conserved among ciliated organisms. A combination of genetic, biochemical and cell biological approaches will be taken. One process under investigation is intraflagellar transport (IFT), which is necessary for the assembly and maintenance of almost all cilia and flagella. I FT involves the movement of particles to the tip of the flagellum and back. These particles contain at least 16 different subunits, but almost nothing is known about the functions of the individual subunits. Studies will characterize Chlamydomonas null mutants defective in two highly conserved IFT-particle proteins, IFT46 and IFT20, to test the hypotheses that IFT46 is involved in transport of the outer dynein arms into the flagellum, and that IFT20 is involved in delivery of membrane proteins to the flagellum. Another process being studied is the mechanism of ciliary and flagellar movement. One protein recently implicated in this process is hydin, a component of the central pair (CP) of microtubules in the Chlamydomonas flagellar axoneme. Hydin appears to have a role in the CP/radial spoke signaling pathway that controls dynein arm activity. Experiments will be carried out to identify the proteins with which hydin interacts in both the CP and the radial spokes. In the mouse and possibly in humans, Hydin defects cause hydrocephalus, which is the lethal accumulation of cerebrospinal fluid in the ventricles of the brain. Studies will use mice defective in Hydin to determine if Hydin also is a CP protein in mammals, and if it is important for ciliary motility in the brain and airway. In related studies, a global analysis of Chlamydomonas CP proteins will be carried out to fill a large gap in our knowldedge of this important structure, and to facilitate studies of hydin and of CP/radial spoke interaction. Another important disease protein being investigated is nephrocystin-4. Defects in Nephrocystin-4 cause cystic kidney disease and retinal degeneration in humans. It is believed to be a protein of the ciliary transition region, but nothing is known about its function. A Chlamydomonas mutant lacking nephrocystin-4 will be characterized to learn more about this protein's specific location and function in the transition region. Defects in the processes and proteins under investigation cause disease in humans and vertebrate model organisms. The research will provide new information on the role of cilia and flagella in cystic kidney disease, retinal degeneration, primary ciliary dyskinesia, male infertility, and hydrocephalus.